1. Field of the Invention
This application relates to apparatus for forming photographic images from digital data and mare particular to a system for rapid and effective adjustment of the optical focusing and modulation components in such apparatus. Systems of this type are used, for example, to generate photographs from digital information collected by means of satellites, aircraft, or other sources. The digital information may be derived by scanning photographic prints or negatives. The distal information, after computer enhancement or other modification of the data, is reproduced in image form for use in such diverse applications as oil and mineral exploration, forestry and agricultural management surveillance, map making, and scientific study of the environment, printing, art, and medical diagnosis.
2. Description of Related Art
Digital imaging systems are in wide use for many applications. Both black and white and full color systems have been developed. In color systems, it is usual to either create a number of separate color beams or to separate an uncollimated white light source into color components by the use of filters. The separate beams are then intensity modulated in accordance with the digital information to be portrayed. A piece of photographic film is placed on a revolving drum where it is exposed to the modulated light beams. The photographic images are formed of small rectangular pixels that are individually exposed to the particular intensity and color called for by the digital data. In the typical color system, three separate beams of light are directed toward the film at different locations. The composite scanning exposure of the three beams produces the appropriate color and intensity at each pixel location. The quality of the prints made in this manner leaves something to be desired.
It is difficult to maintain the positioning of three separate beams with such precision that each pixel, which must be subjected to three successive exposures, is clearly defined and abuts the adjacent pixels without overlapping. In addition to the difficulties of separately controlling the three separate light beams, the rotation of the drum must be maintained with great precision at a constant speed to prevent the pixels from either being spaced apart or overlapping.
There are many advantages in combining the separate color beams into a single composite image which eliminates a number of sources of distortion. Whether the beams are combined or focused separately on the moving drum, the paths of the light beams between the source and the film surface must be controlled with high precision. Each component in the modulation and focusing sequence must be positioned with extreme accuracy. This is particularly difficult because of the interaction between various adjustments. Such adjustment of the beam paths may take from several hours to several days.
Systems have been developed in which the entire optical system can be moved as a unit. For example, U.S. Pat. No. 4,297,713 to Ichikawa et al. describes a laser recording apparatus in which a laser beam is converted and expanded into a collimated beam before being directed toward a recording medium. However, the entire optical system is moved as a unit. A stated purpose of the apparatus is to permit replacement of the entire optical system. The patent does not address the problem of adjusting the optical components relative to each other. It does not offer any solution for the problem's solved by the current invention.
U.S. Pat. No. 4,695,698 to Mayor et al. discloses a laser beam optical system in which individual components are adjusted to create a collimated beam having two separate optical sources. However, the Mayor et al. system does not eliminate the painstaking adjustment procedures because the optical source and a group of successive optical devices are all mounted on the same movable structure. That is, the beam elements as a group cannot be adjusted separately from the optical source other than by individual adjustment of each optical component.